1. Field of the Invention
The present invention relates to an automatic gain control circuit, and more particularly, to an automatic gain control circuit that generates a uniform size output signal regardless of an input signal size.
2. Background of the Related Art
Since size of a signal that is supplied to a receiving unit of a terminal or a communication system varies because of varied distances between relay stations, an automatic gain control circuit is required to output a uniform sized signal. FIG. 1 is a block diagram illustrating a related art automatic gain control circuit that is composed of a variable gain amplifier 10 varying gain of an input signal (Vin) and a control voltage generator 20. The control voltage generator 20 generates a control voltage (Vagc) that is inversely proportional to size of an output signal (Vout) of the variable gain amplifier 10. The variable gain amplifier 10 is composed of a multiplier.
Referring to FIG. 1, the operation of the related art automatic gain control circuit will now be described. When the input signal (Vin) is externally initially applied, the variable gain amplifier 10 outputs the output signal (Vout), which has uniform gain. The control voltage generator 20 receives the output signal (Vout) from the variable gain amplifier 10 and generates a control signal (Vagc), which is inversely proportional to size of the output signal (Vout). The control signal (Vagc) is fed back to the variable gain amplifier 10, which multiplies the external input signal (Vin) and the control signal (Vagc). Thus, the final output signal (Vout) is generated with a uniform size.
For example, if the input signal (Vin) is A sin.omega.t, the final output signal (Vout) can be expressed in equation (1) as follows. ##EQU1## Thus, the final output signal (Vout) has the size of A*Vagc.
As described above, the related art automatic gain control circuit has various problems. It is very difficult to embody a circuit such as the control voltage generator 20 required by the related art automatic gain control circuit that generates the control voltage (Vagc), which is inversely proportional to the size of the output signal (Vout). The control voltage generator required by the related art automatic gain control circuit varies for each system in which it is incorporated.
The above references are incorporated by reference herein where appropriate for appropriate teachings of additional or alternative details, features and/or technical background.